1. Field of the Invention
The present invention relates to an image-shake preventing device suitable for use in an image pickup apparatus, such as a video camera, and capable of correcting a shake (movement) of an image due to a vibration of the apparatus, or the like.
2. Description of the Related Art
An electronic correcting system, an optical correcting system and the like have heretofore been known as a system for correcting a shake of an image in this kind of image-shake preventing device. The electronic correcting system is generally arranged to store in a memory an input image which immediately precedes the current input image, detect a shake of an image by detecting a variation of the image from the current input image and the previous input image stored in the memory, and vary an image reading position in the memory from which to read out a cut-out image so as to cancel the shake, thereby correcting the shake of the image. The optical correcting system generally includes a variable angle prism disposed in front of a lens and is arranged to turn the variable angle prism and bend the optical axis thereof so as to cancel a shake of an image, thereby correcting the shake of the image.
FIG. 1 is a block diagram showing the arrangement of a video camera having an image-shake preventing device of the conventional, electronic correction type. The arrangement shown in FIG. 1 includes an optical system 1 made up of predetermined constituent components, such as a focusing lens group provided for the purpose of focusing, a zooming lens group for varying a focal length of the optical system 1, a compensation lens group, and an iris for adjusting the amount of light. An image pickup element 2 is made up of, for example, a two-dimensional CCD and is provided for converting an input light signal into an electrical signal and outputting the electrical signal. A sample-and-hold (S/H) circuit 3 is provided for sampling and holding the electrical signal supplied from the image pickup element 2, at intervals of a predetermined period, and an automatic gain control (AGC) circuit 4 is provided for controlling the gain of the electrical signal outputted from the S/H circuit 3.
The arrangement shown in FIG. 1 also includes an analog-to-digital (A/D) converter 5 for converting an analog signal outputted from the AGC circuit 4 into a digital signal, a Y/C separation circuit 6 for generating two kinds of delayed signals, i.e., a 1H delayed signal (H: horizontal synchronizing period) and a 2H delayed signal, from the signal outputted from the A/D converter 5, and for performing computations on the 1H and 2H delayed signals to separate the signal outputted from the A/D converter 5 into a chrominance signal C and a luminance signal Y. A C process circuit 7 is provided for generating the chrominance signal C from the 2H delayed signal outputted from the Y/C separation circuit 6, and a Y process circuit 8 is provided for generating the luminance signal Y from the 1H delayed signal outputted from the Y/C separation circuit 6 and performing edge enhancement, gamma correction and other predetermined processes on the luminance signal Y.
The arrangement shown in FIG. 1 also includes a first memory 9 for temporarily storing the chrominance signal C outputted from the C process circuit 7, a second memory 10 for temporarily storing the luminance signal Y outputted from the Y process circuit 8, a first digital-to-analog (D/A) converter 11 for converting the output signal (digital signal) of the first memory 9 into an analog signal, a second digital-to-analog (D/A) converter 12 for converting the output signal (digital signal) of the second memory 10 into an analog signal, a first signal output terminal 13 through which to output the signal outputted from the D/A converter 11, and a second signal output terminal 14 through which to output the signal outputted from the D/A converter 12.
The arrangement shown in FIG. 1 also includes a two-dimensional band-pass filter (BPF) 15 which is a spatial-frequency filter for extracting only a signal having a predetermined frequency band useful for detecting a motion vector, from the luminance signal outputted from the Y process circuit 8, the BPF filter 15 serving to eliminate the high and low spatial frequency components of an image signal which are unsuitable for detecting a motion vector, a motion-vector detecting circuit 16 for detecting a motion vector indicative of movements of an image in horizontal (H) and vertical (V) directions from the output signal of the BPF filter 15, a third memory 17 for temporarily storing the output signal of the BPF filter 15, the output signal of the third memory 17 being inputted to the motion-vector detecting circuit 16, and a memory-reading controlling circuit 18 for controlling the image reading position of each of the first and second memories 9 and 10 on the basis of the output of the motion-vector detecting circuit 16 so that shake of an image in the respective horizontal and vertical directions can be corrected. The image reading position of each of the first and second memory 9 and 10 is shifted in the direction of, and by the amount of a movement indicated by, the motion vector obtained in the motion-vector detecting circuit 16, whereby the movements, i.e., shake, of the image in the horizontal and vertical directions can be cancelled.
The chrominance and luminance signals C and Y, the image-shake of which has been corrected in the above-described manner, are respectively supplied from the first and second memories 9 and 10 to the D/A converters 11 and 12. The chrominance and luminance signals C and Y are respectively converted by the D/A converters 11 and 12 and outputted through the first and second signal output terminals 13 and 14.
FIG. 2 is a block diagram showing the arrangement of a video camera having an image-shake preventing device of the conventional, optical correction type. In FIG. 2, identical reference numerals are used to denote constituent parts identical to those shown in FIG. 1, and description thereof is omitted. Unlike the arrangement shown in FIG. 1, the memory-reading controlling circuit 18 is omitted from the arrangement shown in FIG. 2, and a variable angle prism (VAP) 19 is instead turnably disposed in front of the optical system 1 and a prism controlling circuit 20 is disposed for driving and controlling the variable angle prism 19. The variable angle prism 19 has a structure in which a liquid of high refractive index is charged into the sealed space between two parallel flat plates, and is arranged to be able to change the direction of its optical axis, i.e., its apex angle, by varying the angle made by the two parallel flat plates. The prism controlling circuit 20 includes a vertical-direction control part (V-direction VAP controlling part) 20a for driving and controlling the variable angle prism 19 to correct a movement of an image in the vertical direction thereof and a horizontal-direction control part (H-direction VAP controlling part) 20b for driving and controlling the variable angle prism 19 to correct a movement of the image in the horizontal direction thereof.
A motion-vector detection signal indicative of a motion vector detected by the motion-vector detecting circuit 16 is inputted to the prism controlling circuit 20, and the variable angle prism 19 is driven and controlled by the prism controlling circuit 20 so that shake of the image in the vertical and horizontal directions thereof can be corrected.
However, in an image-shake preventing device which relies on only a conventional electronic correcting system, as shown in FIG. 1, which electronically corrects shake in the vertical and horizontal directions, it is necessary to make an image reading area smaller than the picture size of an image stored in the memory and it is, therefore, necessary to perform processing, such as enlargement and interpolation, for restoring the picture size of a read image to the original picture size. This leads to image degradation which is particularly noticeable in the case of a shake correction in the vertical direction, in which the number of available pixels is small.
In an image-shake preventing device which relies on only the conventional optical correcting system, as shown in FIG. 2, which optically corrects shake in the vertical and horizontal directions, although no substantial image degradation occurs, a special optical system and a control circuit therefor are needed. For this reason, the image-shake preventing device of the conventional optical correcting type has a higher price and a greater power consumption than that of the conventional electronic correcting type.
Japanese Laid-Open Patent Application No. Sho 63-166370 and the like disclose a purely electronic image-shake correcting device which is arranged to store a video signal outputted from an image pickup element (CCD) in an image memory or the like, detect an image shake from information about the video signal to find the amount of displacement of the image, and shift an image reading address of the image memory according to the amount of displacement of the image, thereby correcting the image shake.
It has also been proposed to provide a large-picture (area) image pickup element type of image-shake preventing device which includes a large-picture image pickup element having a larger picture area than a normal image pickup element. This type of image-shake preventing device is arranged to detect a movement by means of an acceleration sensor or the like and control a reading start position of an image which is stored in a field memory, without using a memory and according to a detection signal provided by the acceleration sensor, thereby correcting an image shake.
There is another optical type of image-shake preventing device in addition to the above-described image-shake preventing device which includes the variable angle prism (VAP) and is arranged to detect a movement by means of the acceleration sensor and optically correct an image shake. For example, an inertial pendulum type of image-shake preventing device (U.S. Pat. Nos. 2,959,088 and 2,829,557 and the like) is known. In the inertial pendulum type of image-shake preventing device, an inertial pendulum type of shake preventing lens having a two-axes gimbal structure is disposed around a master lens, and an image shake is cancelled by this shake preventing lens, thereby correcting the image shake.